OP ARTS AND SCIENCES. 



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mination, personal equation, and other causes, greatly exceeds this, 

 especially on au object like a hill-top, on which there is no signal to 

 be observed. 



To study the nature of the variations they have been grouped in 

 Table VI., according to the zenith distance of the sun, the height of 

 the barometer, the height of thermometer, and the logarithm of the 

 correction for temperature and pressure according to Bessel's formula 

 for refraction. In each portion of the table the first column gives the 

 approximate mean value of the argument in each group ; the second, 

 the number of sets ; the third, the mean value of A O. 



TABLE VI. — Grouping of Observations. 



